Heat accumulator and exchanger



June 1951 J. o. JACKSON 2,556,498

' HEAT ACCUMULATOR AND EXCHANGER Filed Feb. 21, 1948 4 Sheets-Sheet 1[Q1 IE? 56 57 INVENTOR.

fM/ll O. J M w June 12, 1951 J. o. JACKSON HEAT ACCUMULATOR ANDEXOHANGER 4 Sheets-Sheet 2 Filed Feb. 21, 1948 June 12, 1951 o, JACKSON2,556,498

HEAT ACCUMULATOR AND EXCHANGER Filed Feb. 21, 1948 v 4 Sheets-Sheet :s

o o o 0 2| o o o o 24 o o o o o o o o o o o Q 32 27 32 o o o o o o 27 I27 o o o o o 24 24 o o o o INVENTOR. (Q gwluw ZMY -MP June 12, 1951 J.o. JACKSON HEAT ACCUMULATOR AND EXCHANGER 4 Sheets-Sheet 4 Filed Feb.21, 1948 1 1: 8 3 iii-572x B M Q a- 7741i) 4/; WW

Patented June 12, 1951 HEAT ACCUMULATOR AND EXCHANGER James 0. Jackson,Grafton, Pa., assignor to Pittsburgh-Des Moines Company, a corporationof Pennsylvania Application February 21, 1948, Serial No. 10,139

14 Claims. 1

This invention relates to heat accumulators and exchangers and one ofits objects is to produce an improved device of this character.

Another object is to produce a heat accumulator and exchanger by meansof which it is possible to heat to a substantially constant temperatureastream of air having a substantially constant pressure and decreasingtemperature.

Another object is to produce a heat accumulator and exchanger having amuch higher exchange coefiicient than any of the prior art devices ofthis type with which I am familiar.

A further object is to produce a heat accumulator and exchanger havingan exchange coefficient of at least about 150 B. t. u.s per square footper hour per Fahrenheit degree temperature difierence between the meantemperature of the air being heated and the temperature of the surfacesof the exchanger with which such air contacts.

A further and more limited object is to produce a heat accumulator andexchanger capable of heating to the desired temperature, the airnecessary for a single run of a blowdown supersonic tunnel, while suchair is flowing from a storage container or reservoir to the nozzle ofsuch tunnel during such run.

These as well as other objects which will readily appear to thoseskilled in this particular art, I attain by means of the structuresdescribed in the specification and illustrated in the drawingsaccompanying and forming part of this application.

In the drawings:

Figure 1 is a diagrammatic view in top plan of a supersonic wind tunnelof the blowdown type, in the make-up of which a heat accumulator andexchanger embodying this invention is utilized.

Fig. 2 is an enlarged top plan view of the heat accumulator andexchanger of Fig. 1;

Fig. 3 is a view in side elevation of the heat accumulator and exchangerof Fig. 2;

Fig. 4 is a sectional elevational view taken on line IVIV of Fig. 2;

Fig. 5 is an enlarged sectional view taken on line VV of Fig. 4. In bothFigs. 4 and 5, the individual tubes are omitted, merely the outline ofthe tube bundles being shown.

Fig. 6 is a view looking toward Fig. 2, from line VIVI but is on anenlarged scale;

Fig. 7 is an end view of one of the hexagonal 2 of the two insulated endgates which are closed during the heat accumulating periods. These gatesare shown open in Fig. 4 and closed in Fig. 6;

Fig. 9 is a view partly in elevation and partly in section of a potheadconnection such as used in the heat accumulator and exchanger of thisinvention;

Figs. 10-14 inclusive are enlarged detail views of parts of such potheadconnection; and

Fig. 15 is a fragmentary cross sectional view of a peripheral rimportion of the gate of Fig. 8.

The heat accumulator and exchanger of this invention in its preferredform comprises a large number of closely packed small diameter steeltubes with which the air or other fluid to be heated is caused tocontact during its passage through the device. Such tubes are arrangedin groups and each such group of tubes has an electric heating elementlocated therein.

In the drawings, which closely follow one installation constructed inaccordance with this invention, the tubes, which are numbered 20, areA;" nominal diameter, iron pipe size, steel tubes 10 feet long. 39,000of these tubes, with their major axes lying parallel are housed within asteel casing having a cylindrical intermediate portion 2| having aninternal diameter of 89 inches and a length of 12 feet and tapered orfrusto-conical end portions 22 and 23.

Tubes 20 are arranged in groups or bundles, fifty-five of which, incross section, are regular hexagons, and six are half hexagons as shownin Fig. 5. Each hexagonal bundle has a short diameter of about ten andone half inches and contains 624 tubes.

A steel tube 24 having an outer diameter of one inch, an internaldiameter of 78 hundredths of an inch and a length of ten feet serves asa housing or container for an electric heating element 24a of the metalsheathed type.

Tube 24 is located at the geometric center of each full hexagonal bundleand at the center of the wide side of each half bundle, as shown in Fig.5. Each full bundle as Well as each half bundle is firmly held in shapeby five metal bands '25 which are six inches wide by one sixteenth inchthick and are evenly spaced throughout the length of the bundles asdisclosed in Fig. 4. These bands are each preferably made in threeparts.

The bundles are made up in the shop, so that the tubes can be handledand transported as bundles. They are also installed or placed within thecasing in the field as bundles.

The bundles are made by stacking the tubes in jigs. The one inch tubes24 for the heating elements are placed in position at the center of thewhole bundles during the stacking of the tubes, and in the case of thehalf bundles, toward the end of the stacking procedure.

After the tubes have been stacked. in the jigs, they are forced intoclose contact with one another by tourniquet-like means which are usedat intervals throughout the length of the tube bundles adjacent thepositions which bands 25 are to occupy. first tack-welded in positionand then permanently welded together. Cooling of the bands and the weldmetal causes the bands to shrink tightly around the tube bundles holdingthe tubes firmly in place.

The tube bundles are supported in place within portion 2i of the casingby means of a cradle consisting of five semi-circular steel members 28,secured in position within the lower half of the casing in line withmetal bands 25v of the tube bundles (Figs. 4 and 5). The innerperipheral edge of each cradle member 26 is shaped so as to conform tothe adjacent faces of the full and half bundles of tubes located withinthe lower part of the casing (Fig. 5). While tubes 2% are omitted fromFigs. 4 and 5, the tube bundles are indicated. Heater housing tubes 24,however, are indicated in Fig. 5.

All of the spaces between the shell of intermediate body portion 2 I ofthe casing and the tube bundles above cradle members 26 are filled withindividual or loose tubes (not shown) of the same diameter and length astubes 20. The spaces between the tube bundles and the shell below thetops of the cradle members 26 are blocked off to air fiow by such cradlemembers so that all of the air flowing through the casing is caused tocontact with the tube surfaces,

Heating elements 24a are one half inch in diameter and 11 feet longonefoot longer than tubes 24so that they project six inches beyond each endof such tubes. These six inch projecting portions are made as coldsections so that the electrical connections can be made. to them.

Each heating element 24a has a power consumption of 3500 watts and isthus rated at 3 kw., and since there are 60 such heating elements, thetotal heater load is 210 kw. on a 441.0 volt, 3 phase, 60 cycle A. C.source.

Electrical energy is supplied to the heating elements through a circuitwhich includes bus bars 27, lead-in conductors 28, connectors 28a, andjumpers 29, all preferably made from stainless steel of the 18-18 type.Lead-in conductors 23 are fed by copper conductors 50 through copperconnecting lugs 48. Bus bars 2'I are supported in position adjacent theinlet or upstream ends of the tube bundles by support brackets 32 whichare secured to the intermediate cylindrical portion 2! of the casing.The bus bars are insulated from such brackets by means of insulators 33(Figs. 12, 13 and 14).

Since the heat accumulator and exchanger of this invention operates atpressures of at least 100 pounds per square inch and temperatures of atleast 500 F., the means for connecting bus bars 2'. to the source ofcurrent supply becomes a problem.

Lead-in conductors 28, which are weld connected to bus bars 21, extendoutwardly through an opening in the cone-shaped wall of upstream end 22of the casing. Conductors 28 which are about 1% inches in diameter arestraight and The sections of bands 25 are parallel for a distance or"about six feet and are arranged in a triangular group as shown in Fig.11. The straight portion of the triangular group is housed within asteel tube 34 (Fig. 9) about five inches in diameter. This tube at itsinner end is provided with a welded on flange 35 which is bolted to acompanion flange 36 welded to the end of a short tube section ii whichextends within the opening in the wallof cone-shaped end 22 and iswelded in place within such opening. The outer or distal end of tube 34is provided with a flared section 38 preferably welded thereto, and thismember 38 at its outer end is provided with a flange 39. Member 38 formsone part of a pothead which comprises member 35, a corresponding member40, having a flange 4i, and a circular diaphragm 42 secured in placebetween flanges 39 and 4| by means or" a circular row of bolts 43 whichextend through openings in such flanges and such diaphragm.

Diaphragm 42 is preferably formed from a material such as Micarta and isapproximately 18 inches in diameter and 1 inches thick, since it issubjected to the pressure within the casing of the device.

The portions of conductors 28 located Within the pothead are spreadapart as shown in Figure 9 and each such conductor is welded to the headid of a bolt-like lug member 45 (Fig. 10) which extends through anopening formed for its reception in diaphragm 42. A flexible gasket 46is interposed between head 44. and diaphragm 52. Each lug member 45 isthreaded to receive a nut ii and a threaded copper lug 48.; a metalwasher ii being interposed between diaphragm i2 and nut i'i. After nuts4'! clamp lug 45 to diaphragm 5-2, copper lugs 48 are tightened on lugmembers 45. and the lead-in cables 50 are then silver soldered to lugs48.

Tube 3 2 is filled with disk-like electrical insulating members 51.These members are provided with three circular holes arranged to receiveconductors 28; the insulating members 5| being slipped over the threeconductors 28 and slid to position within tube 34 before such conductorsare welded to the bus bars. Members 51 are preferably molded from somematerial which is a heat conductor as well as an electrical insulator; amaterial such as synthetic mica.

The distance from diaphragm 42 to the end 22 of the casing is at leastsix feet, so that the heat transmitted from the accumulator by tube 35and conductors 28 is sufficiently dissipated by the time it reachesdiaphragm 42. as not to be harmful to such diaphragm.

The heat accumulator and exchanger ofthis invention was primarilydesigned to be part of a supersonic wind tunnel of the blowdown type,and Figure 1 of the drawings as before pointed out is a diagrammatic topplan view of such wind tunnel.

In Figure 1, 52 represents the. heat accumulator and exchanger, 53represents the source of supply of stored air under pressure, 54represents the expansion nozzle of. the wind tunnel and 55 representsthe test section of the tunnel. For the purposes of simplification,Figure 1 shows a window 56 in the top of the test section instead ofwindows in opposite sides of such section. 51 represents the sectionconnecting the circular downstream end of the heat accumulator andexchanger to the square inlet to nozzle 54. This serves as the stillingsection for the nozzle. 53 represents an automatic valve formaintaining, at a substantially constant pressure, the air deliveredfrom source 53 (the storage tank or tanks) to the upstream end of nozzle54.

The air to be heated enters the heat accumulator and exchanger throughport 59 (Fig. 4) of the upstream end 22 and the heated air leavesthrough port 60 of the downstream end 23.

Because of the fact that the tubes nearest the electrical heatingelements become hotter than those further away and also because of thefact that after each blowdown or each heattransfer period, there is amarked temperature difference between the opposite ends of the tubebundles; the upstream ends having the lowest temperature and thedownstream ends having the highest, it becomes desirable to equalize thetemperatures both transversely and longitudinally of the stack of tubebundles and loose tubes within the heat accumulator and exchanger.

= In order to obtain this equalization of temperatures, I close endports 59 and 50 of the device during each heat accumulating period andcause the air thus trapped within the casing of the accumulator andexchanger to circulate again and again preferably in the oppositedirectionto the normal flow. In order to do this, I employ a gate 6| forport 59 and a gate 62 for port 60. These gates are actuated either bymotors 63 or by hand 'wheels 64. An air duct system, which as anentirety is numbered 65,

connects conical end portions 22 and 23 of the casing and is providedwith shut-off valves 66 and 6'1 and a blower 68 driven by a motor 69.

During a heat accumulation cycle, valves 66 and 61 are opened and blower68 draws air from end portion 22 of the device and delivers such air toend portion 23. Because of this arrangement, the air trapped within thedevice by the closing of end gates 6| and 62 is caused to continuallycirculate through the stack of tubes as long as valves 66 and 61 areopen and blower 68 operates.

Gate 6 l which controls port 59 at the upstream end of the casing, isabout 36 inches in diameter, while gate 62, which'controls port 60 atthe downstream end of the casing, is about 60 inches in diameter. Thesegates are of similar construction and a description of one, therefore,is deemed sufficient.

A shaft 'II which carries the gate is journaled in bearings indicated at12 (Figs. 2, 3 and 6) and is surrounded by a hollow shaft '53 whichforms part of what might be termed the gate frame as will later appear.The gate is provided with a bar rim 74 (Fig. 15) and the inner portionof this rim has its sides cut away forming a central flange 15. A numberof parallel ribs (not shown) extending at right angles to the axes ofshafts H and 13, have their inner ends welded to hollow shaft 13 andtheir outer ends welded to the inner peripheral edge '16 of flange l5.

. Cover plates W and 78 which are preferably formed from inch steelplate bear against the side faces of flange l5 and are welded to rim 14,to hollow shaft 13 and to such ribs. I-Iollow shaft #3 and solid shaft Hare secured together by five tapered pins 19 as shown in Figs. 6 and 8.

After one cover plate is thus secured in position, the interior of thegate is packed with suitable thermal insulating cement. After the cementis thoroughly dry, the other cover plate is welded in position, carebeing taken to allow any moisturewithin the gate to escape as thewelding of this second cover to the ribs, rim and hollow" shaftprogresses.

Openings are made in this second cover plate at different positionsopposite the ribs and it is because of these openings that this coverplate can be welded to the ribs.

As shown in Figs. 4 and 5, the casing of the device is covered with arelatively heavy layer of heat insulating material 70. This and theinsulating material for the circulating system 10a is indicated bydotted lines in Fig. 2.

Under some circumstances, it may be necessary to operate the accumulatorand exchanger at a much higher temperature than 500 F. If it is to beused in heating the air for a supersonic wind tunnel of the blowdowntype in which velocities much above a Mach number of 4.4 are to be used,it may be desirable or necessary to use refractory tubes or otherrefractory members instead of steel tubes as the heat absorbing ele-.The necessary air temperatures may be ments. well above 2000 F.

In the installation above referred to, the .air is delivered from thestorage tanks at a diminishing pressure and temperature.

hour heat accumulating period and to deliver such heat energy to the airstream during a ten second operating period.

During such operating period, heat stored in the tubes is transferred tothe air at a rate of 354,000,000 3. t. uis per hour. About 8460 poundsof dry air at an average temperature of 57 F. are heated during this tensecond period to an average temperature of 508 F. The exchangecoefficient, usually referred to as the H value, is B. t. u.s per squarefoot per hour per Fahrenheit degree temperature difference between themean temperature of the tubes and the air being heated, as compared witha coefficient of from 5 to 15 as ordinarily obtained in commercial heatexchangers.

I obtain the extremely high exchange coefficient of 155 by takingadvantage of the fact that a pressure loss in the air being heated,which would be prohibitive in commercial applications as uneconomical,is not objectionable in the operation of a supersonic wind tunnel of theblowdown type, because the air is stored at a pressure almost doublethat at which it is delivered to the nozzle of the tunnel.

In the installation above referred to, the air is stored at over 200 p.s. i. and is used in the tunnel nozzle at about 117 pounds per squareinch absolute, while the pressure drop through the exchanger is only tenp. s. i. In other words, in order to store sufficient air for theoperation of the tunnel, it is necessary to increase the pressure, andsuch increased pressure is advantageously used to obtain the verydesirable high thermal exchange coeliicient in the accumulator andexchanger.

Operation When the heat accumulator and exchanger is first put inoperation, it requires about nine hours to raise its temperature fromaround 70 F.

to a required average temperature of about Such air on its Way; to theheat accumulator and exchanger, passes 7 546 25'. However, due to thefact that the device in heating the proper amount of air to the desiredtemperature for a blowdown gives up but a small part of its stored B. t.u.s, it takes a much shorter period of time for subsequent heatmgs.

When the heat storage tubes are heated to an average temperature ofabout 546 F., the required amount of air for a ten second blowdown canbe heated to a temperature of from 500 to 510 F. during such ten secondperiod.

In the installation above referred to, it is necessary .to operate theair compressors about four hours in order to obtain a pressure of 205pounds per square inch gauge in the storage tanks.

During this four hour period, the heating elements are energized forabout the first hour and one half during which a little more than thetotal required amount of heat for one blowdown ofthe wind tunnel isdelivered to the stacked tubes within the heat accumulator andexchanger. After this, the power is shut on.

While the heating elements are being energized, end gates 61 and E52 areclosed, valves .66 and 81 are opened and blower 68 is operated by itsmotor 69 to circulate the air in the opposite direction to the normaldirection of flow through the device during a blowdown.

The tubes nearest the heating elements of course become hotter than theother tubes in the bundles and I have found that in order tosubstantially equalize the temperature of the tubes, it is necessary tooperate blower 63 for about four hours, which time can be made tocoincide with the operation of the compressors.

The function of the air circulation is to transfer heat from the Warmerto the cooler tubes and to equalize the temperature of the tubes bothlongitudinally and throughout the cross section of the accumulator andexchanger.

The action of the air passing through the accumulator and exchangerduring a ten second blowdown is as follows:

The first air flowing through the heated accumulator and exchangerabsorbs more heat from the upstream ends of the tubes than it does fromthe mid sections and very much more than it does from the downstreamends. In fact, the first air probably absorbs no heat Whatever from thedownstream ends of the tubes. As the flow continues, the temperature ofthe upstream ends of the tubes falls, while that of the mid sections isbut slightly reduced.

In general, the longer the tubes are the longer the time and the greaterthe volume of air that may be passed through them for a given outlettemperature drop. I have found that for a ten second run in a tunnelhaving a velocity of Mach 2 and a throat area of five square feet, it ispossible to maintain a constant exit temperature within or -5 Fahrenheitdegrees.

At the end of a blowdown period, the upstream ends of the tubes are muchcolder than the downstream ends and for this reason,.the air during theheating up period is circulated in a direction opposite to the normaldirection of flow.

At the end of a ten second blowdown, the temperature of the upstream endof the tubes drops about 238 Fahrenheit degrees; the temperature midwaybetween the ends of the'tubes drops about 50 Fahrenheit degrees and thetemperature adjacent the downstream ends drops only about 1 -Fahrenheitdegree.

As above pointed out, the length of the cylindrical portion of theexchanger, in the installation above referred to is twelve feet and itsinside diameter is 89 inches. The cross sectional area, therefore is 43square feet. The metal area of the tubes equals 45 percent of such 43square feet. The tube hole area equals 40 percent and the area of thespaces between the tubes equals 15--percent of such 43 square feet. Theaverage velocity of the air flowing through the device during a blowdownis 161 feet per second.

What I claim is:

1. In a heat accumulator and exchanger, a hollow casing having anintermediate portion and ported end portions adapted to be connectedinto a fluid line, a mass of heat absorbing material substantiallyfilling such intermediate portion and having openings therethroughconnecting such end portions, a number of tubes arranged in spacedpositions Within such mass and each extending from one such end portionto the other and an electric heating element located within each suchtube and having an effective heating length which is substantially thesame as that ofsuch tube.

2. In a heat accumulator and exchanger, a hollow casing having anintermediate portion and portedend portions adapted to be connected intoa fluid line, amass of heat-absorbing material substantially fillingsuch intermediate portion and having openings therethrough connectingsuch end portions, a number of heating agents arranged at spacedpositions within such mass, gates forcontrolling the ports of the endportions, a fluid duct independent of the openings insuch mass forconnecting such end portions, and means for circulating the heated fluidconfined within such casing by the closing of such r s- 3. In a heataccumulator and exchanger, an elongated hollow casing having anintermediate portion and ported end portions adapted to be connectedinto a fluid line, groups of contacting metal tubes substantiallyfilling such intermediate portion and providing multiple passagesbetween such ported end portions, and an electric heating elementlocated adjacent the center of a major portion of such groups, extendinglengthwise of such tubes and having substantially the same length as thelength of such tubes.

d. In a heat accumulator and. exchanger, a casing having an intermediateportion and ported end portions adapted to be connected into a fluidline, multiple groups of metal contacting tubes located within,substantially filling such intermediate portion and connecting such endportions, and electric heating means located within, extendinglengthwise of each such group tubes and having an effective heatinglength substantially equalling the length of such tubes; the tubes ofeach such group being bound together so that they can be handled as aunit.

5. In a heat accumulator and exchanger, a metal casinghaving anintermediate portion and end portions adapted to be connected into afluid line, multiple hexagonal bundles of metal tubes ofrelatively'small diameter located'within, substantially filling suchintermediate portion and connecting such end portions, and an electricheating element located within and extending lengthwise of each suchbundle.

6. In a heat accumulator and exchanger, a casing having a cylindricalintermediate-portion and tapered'end portions, multiple bundles of metaltubes of relatively small diameter located withinand substantiallyfilling such cylindrical portion and connecting such end portions, andan electric heating device associated with and extending lengthwise ofeach such bundle for heating the tubes thereof; the majority of suchbundles being hexagonal in cross section.

7. In a heat accumulator and exchanger, a metalcasing having acylindrical intermediate portion and tapered end portions, multiplehexagonal bundles of metal tubes of relatively small diameter locatedwithin and substantially filling such cylindrical portion and connectingsuch end portions and an electric heating device associated with eachsuch bundle and having an effective heating length substantially equalto the length of such tubes such heating device being located within andadjacent the center of a majority of such bundles; the tubes of eachbundle being bound together so that they can be handled as a unit.

8. In a heat accumulator and exchanger, a casing having an intermediateportion and end portions having ports therein, gates controlling suchports, a mass of heat absorbing material substantially filling suchintermediate portion and having opening therein connecting such endportions, electric heating elements distributed throughout such mass, afluid duct connecting such end portions outside of such casing, andmeans utilizing such duct for circulating through such mass the heatedair confined within such casingi by the closing of such gates, for thepurpose of equalizing the temperature throughout such mass.

9. In a heat accumulator and exchanger, a casing having an intermediateportion and end portions having port therein, gates controlling suchports, a mass of heat absorbing material substantially filling suchintermediate portion and having openings therein connecting such endportions, electric heating elements located at spaced positions withinsuch mass, a fluid duct connecting such end portions outside of suchcasing, and means utilizing such duct for circulating through such massthe heated air confined within such casing by the closing of such gates,for the purpose of equalizing the temperature throughout such mass.

10. In a heat accumulator and exchanger, a casing having an intermediatebody portion, end portions having ports therein adapted to be connectedinto a line leading from a source of air under pressure, gatescontrolling such ports, multiple groups of metal tubes of relativelysmall diameter located within and substantially filling such bodyportion and extending toward such end portions, electric heatingelements associated with a majority of such groups for heating the Fri)10 tubes thereof, a fluid duct independent of such tubes for connectingsuch end portions, and means within such duct for circulating the airconfined Within such casing by the closing of such gates, for thepurpose of equalizing the temperature in the tubes of such groups.

11. A unit for use in making a heat accumulator and exchanger,comprising a bundle of metal tubes of relatively small diameter incontact with one another, grouped about an electric heating element,extending in the same direction and having an effective heating lengthwhich is substantially the same as that of such tubes.

12. A unit for use in making a heat accumulator and exchanger,comprising a hexagonal bundle of annular metal tubes of relatively smalldiameter, contacting with one another throughout their length andgrouped about an electric heating element extending in the samedirection and having an effective heating length which is substantiallythe same as that of such tubes.

13. A unit for use in making heat accumulator and exchanger, comprisinga hexagonal bundle of annular metal tubes of relatively small diametergrouped about a metal tube of larger diameter enclosing an electricheating element having an eifective heating length which issubstantially the same as that of such tubes and means for bindingtogether the tubes of such bundle in metal to metal contact.

14. A unit for use in making a heat accumulator and exchanger,comprising a hexagonal bundle of annular metal tubes of relatively smalldiameter grouped about a metal tube of the same length but of largerdiameter and which encloses a sheathed type electric heating elementhaving an effective heating length which is substantially the same asthat of the tubes of such bundle and has cold ends projecting beyond theends 01 such tubes and bands spaced longitudinally of such bundlebinding such tubes in contact with one another throughout their length.

JAMES o. JACKSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 927,173 Schluter July 6, 19091,701,096 Bowling et al Feb. 5, 1929 1,705,812 Fisher Mar. 19, 19291,927,959 Soloos Sept. 26, 1933 2,003,496 Roe June 4, 1935 2,266,257Osterheld Dec. 16, 1941 2,367,170 Fahrenwald Jan. 9, 1945 2,438,670MacDonald et al. Mar. 30, 1948

